The invention relates to a clamping collar.
Such a collar can be used to connect pipes, in particular in the automobile industry or in the aircraft industry (e.g. to connect pipes of the exhaust system or of the system for depolluting combustion gases).
More particularly, the invention relates to a clamping collar of the type comprising:                a belt comprising a strip and two free ends, at least one of said free ends being curved back to form a loop, said loop being defined by an outer belt portion and by an underlying inner belt portion; and        a tightening system suitable for co-operating with said loop so as to tighten said belt.        
Generally, both of the free ends of said belt are curved back so as to form respective loops, and said tightening system makes it possible bring said loops closer together for tightening said belt.
DE 3926626 A1 describes a connection for pipes with two clamping collars of this type. Each of the collars is such that the ends of the belt are curved back towards the outside of the collar, and are then welded or otherwise bonded to the outside face of the strip of the belt, so as to form loops. In addition, each collar has a tightening system with two cylindrical retaining pieces that are received inside respective ones of the two loops of the collar. Such retaining pieces can be referred to as “blocks” or as “gudgeons”.
The first block is provided with a tapped through hole and the second block is provided with a smooth through hole. The tightening system further comprises a screw having a threaded shank and a screw head. Each loop of the collar is provided two openings that are in register with each other so that the shank of the screw passes through each of the two loops. In addition, the shank of the screw passes freely through the smooth hole and engages in the tapped hole. While the screw is being screwed into the first block, the screw head comes into engagement with the second block which then pushes against the inner belt portion of one loop, while the first block pushes against the inner belt portion of the other loop. The collar is thus tightened by bringing said loops closer together.
An object of the invention is to propose a clamping collar of the above-mentioned type that is not provided with any blocks, so as to limit the number of parts of the collar and, also, so as to simplify assembly thereof, and/or so as to reduce the manufacturing cost thereof, while also maintaining good clamping performance.
This object is achieved by a clamping collar of the above-mentioned type in which at least one free end of the belt that forms a loop is curved back towards the inside of the collar, in which the inner belt portion of the loop is extended beyond the loop, under said strip, and in which the outer belt portion of each loop presents a tightening wall with which the tightening system comes into engagement.
Since the tightening system comes into engagement with the tightening wall of the outer belt portion, it is not necessary for a block to be present inside each loop.
In addition, with the collar of the invention, and unlike with the collar of DE 3926626 A1, the forces exerted on the loop by the tightening system are no longer exerted on the inner belt portion, via the inside of the loop, but rather they are exerted on the outer belt portion, via the outside of the loop. In order to take account of this new distribution of the forces, the ends are curved back towards the inside of the collar so that the strip of the belt is extended via the outer belt portion (rather than via the inner belt portion as in DE 3926626 A1).
Advantageously, in order to simplify manufacturing of the collar and, in particular, so as not to have to perform welding or other bonding operations, said inner belt portion is not fastened under said strip.
This is possible firstly because the tightening forces are exerted on the outer belt portion of the loop and secondly because said inner belt portion is held stationary by being compressed between the article to be clamped and the strip that covers said inner belt portion. While the collar is being tightened, friction forces are generated between the article to be clamped, said inner belt portion, and the strip. Said friction forces can be sufficient to prevent any movement of the inner belt portion and thus to oppose deformation (flattening) of the loop.
However, if said friction forces are insufficient, an abutment is provided for preventing the inner belt portion from moving along the strip (i.e. in the circumferential direction of the belt) while the collar is being tightened. In a simple embodiment, said abutment is formed by a shoulder against which said inner belt portion comes into abutment, while the collar is being tightened. In addition, a shoulder of height substantially equal to the thickness of the inner belt portion makes it possible to guarantee that the clamping outline of the collar is continuous.
Naturally, it is possible to imagine other types of abutments, e.g. a lug or a rib projecting from the inside face of the strip, or indeed a lug or a rib integral with the inner belt portion, projecting into the loop and coming into abutment against the base of the outer belt portion.